The present invention relates to a method for forming piston pins, and more particularly a method for forming piston pins in one or multiple operations having tapered internal openings. The present invention also includes the tapered piston pin made utilizing this process.
Reciprocating internal combustion engines generally use pistons that oscillate in the cylinder. As illustrated in FIG. 1, the piston 12 functions as a sliding plug that fits closely inside the bore of a cylinder. Essentially, the piston is driven alternately in the cylinder. The burning of a mixture of fuel and air above a piston generates gas pressure from compressed and ignited combustion gases. This pressure forces the piston in a downward direction. As this happens, the piston transmits the force of expanding combustion gases through the piston pin 10 to the connecting rod 14. The piston is attached to the connecting rod, and thus to the crankshaft, transferring reciprocating motion to rotating motion.
Piston pins form an important part of the reciprocating internal combustion engine system. Each piston pin extends through aligned openings in the piston and the connecting rod, to establish a pivotal connection between the rod and the piston. As the engine crankshaft rotates, one end of each connecting rod orbits around the crankshaft axis. The other end of the connecting rod has swivel motion around the pin within the piston, whereby each piston delivers power through the connecting rod to the crankshaft. Each piston pin serves as a pivotal connection between the connecting rod and piston.
The forces imposed on the piston, piston pin and connecting rod from combustion are enormous. In addition, piston assemblies (pistons, piston pins and the connecting rods discussed above) account for a large amount of the friction losses in an engine's performance. There is a trend in engine design to reduce the reciprocating mass of the piston assembly including the crankshaft. Thus performance can be enhanced by having a lighter piston pin, which reduces inertial losses, thereby improving engine efficiency. Accordingly, being lightweight is an essential characteristic of an effective piston pin and piston assembly. In addition, the ideal piston pin possesses other important characteristics: wear resistance, rigidity and high strength for withstanding the extreme forces that result from the combustion process. One method of reducing the weight of the piston pin is to reduce the mass at the ends of the internal diameters of the pin by creating an outwardly tapered internal portion.
Certain piston pins are formed with a center web near the middle of the pins as illustrated in FIG. 3. These piston pins are referred to as center webbed, two way extruded or two way formed piston pins. Other piston pins carry weight reduction even further by forming the web on the end of the pin as illustrated in FIG. 4. In this method the web is completely removed for further mass reduction benefits. These pins are commonly referred to as webless, end web, one way extruded or one way formed piston pins. Both piston pin manufacturing methods can also be designed to have tapered bores to reduce weight. Current art is to machine the internal taper into the pin or to extrude a taper into the internal portion of a center web pin. Additionally, some tapers will be added to one way formed pins by adding the tapers in the internal portion through secondary machining or forming operations. These additional operations may include any combinations of annealing, lubrication applications, and secondary forming operations. None of these methods are cost effective nor optimize weight reduction. All of these methods are very expensive.
As stated above, the prior art suffers various deficiencies relating to low efficiency, high costs and sub-optimal weight reduction. There is a need for a cost effective manufacturing method to form center web or webless tapered piston pins in one forming sequence of a machine. In addition, there is a need for an improved and more economical method for forming internal tapers on a piston pin.